This July 8, 2013, photo shows wrecked oil tankers and debris from a runaway train in Lac-Megantic, Quebec, Canada. U.S. transportation officials say the oil industry is not giving up information needed to gauge the danger of moving crude by rail. Several oil train accidents, including one in Quebec, have highlighted the explosive properties of crude coming from booming oil shale fields on the Northern Plains.

BILLINGS, Mont. — U.S. transportation officials rebuked the oil industry Friday for not giving up information regulators say they need to gauge the danger of moving crude by rail, after several accidents highlighted the explosive properties of fuel from the booming oil shale fields on the Northern Plains.

Department of Transportation officials told The Associated Press they have received only limited data on the characteristics of oil from the Bakken region of North Dakota and Montana, despite requests lodged by Secretary Antony Foxx more than two months ago.

“The overall and ongoing lack of cooperation is disappointing, slows progress and certainly raises concerns,” the agency said in a statement. “We still lack data we requested and that energy stakeholders agreed to produce within 30 days.”

The DOT said “a handful of individual companies” have offered the information being sought but would not provide specifics.

Representatives from the American Petroleum Institute refuted the foot-dragging accusation.

“We’d like to know what information they’re not getting so we can give it to them,” said API spokesman Eric Wohlschlegel.

API president Jack Gerard said oil companies have been encouraged by the group to share what they know. He said there’s more data to come, but added that API does not serve as an industry “library” so it would come from multiple sources.

There have been at least four major accidents involving trains carrying crude from the Bakken since production began to boom in 2008. Among them was a derailment last July that killed 47 people and torched a large section of downtown Lac-Megantic, Quebec.

The combustibility of the crude in Lac-Megantic was comparable to gasoline, according to Canadian investigators.

Other accidents with explosions have occurred after derailments of oil trains in Alabama, North Dakota and Oklahoma.

The string of accidents led regulators to warn emergency responders and the public in January that Bakken oil — a light, sweet crude that has high amounts of natural gases and other volatile compounds — could be more dangerous than many conventional crudes.

Some crudes from elsewhere in North America and around the globe share similar volatile properties.

But the Bakken fuel is the first to be moved in North America in modern times in such massive quantities by rail. That’s exposed a new set of safety concerns, including a well-known defect in tens of thousands of rail cars that leads them to rupture in accidents.

Mile-long oil trains can carry 3 million gallons of crude per shipment. The number of carloads delivered by major U.S. railroads has surged astronomically: from 9,344 delivered in 2008 to 434,000 carloads last year. The shipments are delivered to refineries across the U.S. and Canada, including in the Pacific Northwest, California, and the East and Gulf Coasts.

Unlike most hazardous materials produced by chemical plants or other manufacturing sources, crude oil is not refined before being loaded onto trains. As a result, its properties can vary greatly among shipments. Three companies were hit with proposed penalties totaling $93,000 in February for misclassifying oil from the Bakken as less dangerous.

Through the petroleum institute, the industry also has pledged to work with the government to come up with new standards for testing the oil to make sure it’s being handled properly when loaded onto trains.

That process is expected to take several more months, and will be driven in part by what’s learned regarding volatility.